We’ve got iTunes.
We’ve got the Amazon.com MP3 download service (rolls right off the tongue, doesn’t it?).
What about cnet?
It’s been a while since I checked this one out, but I did recently. C|net took over what used to be the old mp3.com site. It was one of those sites that had tons of free music but went belly up (much like riffage.com) due to copyright crap, the RIAA getting in the way and, maybe, being about 4 years too early.
The only thing I could compare it too is last.fm, but without the hard core social aspect. Otherwise, it’s a great place to find music